A charging device for a motor vehicle, having a charging unit which is designed to charge a battery of the motor vehicle, is known from DE 10 2011 016 532 A1. Diagnosis means, by means of which the functionality of the charging unit can be tested, are provided. For this purpose, a test voltage is coupled into an AC input of the charging unit and voltages caused by the test voltage are measured at different measurement points of the charging device. It is possible to test individual assemblies of the charging unit using the diagnosis means. It is not possible to test individual electronic components.